The invention relates to a pressure driven device with a dampening feature at the piston end, especially that of a pneumatic or hydraulic working cylinder.
In accordance with IPC (International Patent Classification) pressure driven devices are classified under IPC F15B15/00, in which details for delaying the stroke are listed under IPC F15B15/22. A delaying or dampening of the stroke of a piston may be achieved by means of the pressure medium itself. The dampening force in such a case is achieved by an appropriate counterpressure on the piston which should preferably be proportional to the speed of movement of the piston. Beside an actively guided (controlled) pressure medium there is also a passive variation in which the pressure medium passes through a throttle. In such a case there is an approximately propolional relation between the pressure medium passing the through throttle and the pressure differential on both sides of the throttle. The factor of proportionality as a characteristic value is essentially determined by the geometry of the throttle.
The desired throttling effect should not commence until the stroke of the piston approaches the end position. Accordingly the flow conditions in the cylinder must change depending on the positioning of the piston within the cylinder, especially in relation to the end of stroke positioning. This may be achieved by different measures.
One possibility consists of changing the outlet, as described in the publication DE 2206410, in which the effective cross-section of the outlet is reduced by the entry of a forward projection of the piston. A known similar solution is embodied in publication DE1925166A, in which a part of several outlets arranged in a parallel configuration are blocked by the piston itself. By applying a suitable arrangement or dimensioning different dampening functions can be realised.
Another possibility is presented by providing a dampening space which is located in relation to the piston movement behind the actual outlet. On the piston advancing into the dampening space the only way of discharging the pressure medium located in the damper space to the actual discharge outlet is by passing through the throttle.
Based on the latter there are a multitude of executions known in which the throttle interconnects to the outlet by special channels which are incorporated into the piston or the cylinder. The utilisation of the free space between piston and cylinder as throttle is also known.
In accordance with publication DEGM6943765 the throttle itself is formed by means of an annular gap between the piston and the cylinder and causes the characteristic value in relation to the piston advancement to stay constant.
A known publication U.S. Pat. No. 4,425,836 utilises a helical recessing on the piston surface as a throttle. By the advance of the piston into the dampening space the characteristic values of the throttle geometry are changed in line with the effective length of the advance and increase in a linear manner to this. The linear increase of the characteristic value may be disadvantageous, unless constructively extensive helical structures and/or cross sections are implemented to facilitate variably increasing characteristic values.
The publication U.S. pat. No. 4,207,800 also refers to the application of a special dampening element which is arranged in the form of a ring between the cylinder and the piston (piston ring). On the front end it exhibits a multiplicity of radially open channels which are also capable of a slight axial shift and rests in the course of the throttling on the opposing annular tee slot of the piston, thus causing the pressure medium to flow through the throttling channels on its way to the outlet below and behind the throttle ring. The advantage of such a modular solution lies in the simple exchangeability of the throttle ring. The disadvantage of the solution lies in constant throttle characteristics in relation to the piston positioning.